The retina of the human eye contains millions of light -sensitive receptors called rod cells and cone cells.
There are about 120 million rod cells in each eye.There is only one type of rod cell so it is only capable of distinguishing between dark and light and the image is seen in black and white. Rod cells are sensitive to low light intensities. They contain a pigment called rhodopsin which breaks down at low light intensities. A number of rod cells are connected to a single bipolar cell (retinal convergence) so that there is a greater chance that the threshold potential will be exceeded and lead to a generator potential due to summation.
There are about 120 million rod cells in each eye.There is only one type of rod cell so it is only capable of distinguishing between dark and light and the image is seen in black and white. Rod cells are sensitive to low light intensities. They contain a pigment called rhodopsin which breaks down at low light intensities. A number of rod cells are connected to a single bipolar cell (retinal convergence) so that there is a greater chance that the threshold potential will be exceeded and lead to a generator potential due to summation.